/Engine/Plugins/Protocols/MQTT/Source/MQTTCore/Public/MQTTClientObject.h
OutMessageId can be used to match this request with the callback response.
[UFUNCTION](Programming/UnrealArchitecture/Reference/Functions)(BlueprintCallable, Category="MQTT") void Publish ( const [FString](API\Runtime\Core\Containers\FString) & InTopic, const [TArray](API\Runtime\Core\Containers\TArray)< uint8 > & InPayload, [EMQTTQualityOfService](API\Plugins\MQTTCore\EMQTTQualityOfService) InQoS, const bool bInRetain )